Contamination in EMs: Introduction, Applications & Drawbacks
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In EM systems, there can be various contaminations:
        i) Specimen contamination.
        ii) Contamination of apertures.
        iii) Vacuum contamination.
        iv) Contamination of electron guns.
        v) Contamination of GIF system in TEMs.

The contamination spots on specimens provide some useful applications, for instance:
         i) Measure the thickness of TEM specimens,
         ii) Trace the specimen drift.

Modern AEMs (analytical electron microscopes) have relatively clean vacuum systems, with residual hydrocarbons in the specimen region being <10-10 torr. However, it is still possible to build up hydrocarbon (HC) and carbon (C) contaminants on the specimens. In general, there are many drawbacks induced by the contamination on specimens, for instance:
         i) Preferentially absorb low-energy X-rays emitted from the specimen. This effect is especially harmful when analyzing light elements.
         ii) Increase the X-ray and EELS background and thus reduce the signal-to-background ratio.